Process for carbonized cellulose fiber or the products thereof

ABSTRACT

Cellulose fiber or the product thereof is treated with a strength increasing agent selected from the group consisting of (A) ammonium sulfate, ammonium bisulfate, ammonium sulfite, ammonium bisulfite, ammonium thiosulfate, ammonium sulfamate, ammonium imidosulfonate, and mixtures thereof; (B) a mixture of at least one compound selected from the group consisting of ammonium sulfate, ammonium bisulfate, ammonium sulfite, ammonium bisulfite, ammonium thiosulfate, ammonium sulfamate, and ammonium imidosulfonate with at least one organic nitrogen base; and (C) a mixture of an organic nitrogen base and an acid selected from the group consisting of sulfuric acid, sulfurous acid and sulfamic acid, and heat treating the product in an inert atmosphere at a temperature of at least about 400* C. for a period of time sufficient to bring about carbonization.

0 Minted States Patent 1151 3,639,140 Miyamicllli 5] lFeb. 1, 11972 [54] lPllNl/(IESS FQR CARBONHZED 3,333,926 8/1967 Moyer et a1 23/209 4 CELLULUSE FIBER OR THE 3,441,378 4/1969 Didchenko .23/209 4 PRQDUCTS THEREOF 3,461,082 3/1969 Otani et a1. .23/209 4 3,479,150 11/1969 Gutzeit .23/209 4 [72] Inventor: Kazuo Miyamichi, Koriyama-shi, Japan 3,479,151 1 1/1969 Gutzeit 1 17/46 CB 3,527,564 9/1970 Moore et a1. ..23/209.5 [73] Assgnee- 523: Fukusmmwsm, 3,532,466 10/1970 Johnson et al. 23/2094 [22] Filed: Oct. 3, 1969 Primary Examiner-Murray Katz q Assistant Examinerl\ l. Sofocleous [2]] Appl' N05 8635 Attorney-Irons, Birch, Swindler& McKie 30 Foreign Application PliOl'itY 111116 [571 ABSTRACT 061. 12, 1968 Japan ..43/74455 Cellulose fiber of the Product thereof treated with a Strength Sept. 5, 1969 Japan... increasing agent selected from the group consisting of (A) am- SEPL 5, 1969 Japan. monium sulfate, ammonium bisulfate, ammonium sulfite, am- Sept. 5 1969 Japan ..44/70439 monium bisulfite ammonium thiosulfatei ammmium Sulfa mate, ammonium imidosulfonate, and mixtures thereof; (B) a [52] USJCH g 117/46 CB 117/228 23/209 l mixture of at least one compound selected from the group 23/2094 8/1162 consisting of ammonium sulfate, ammonium bisulfate, am- [51] 1m CL 4 31/67 rnonium sulfite, ammonium bisulfite, ammonium thiosulfate, [58] Fieid CC ammonium sulfamate, and ammonium. imidosulfonate with at 4 209 16 least one organic nitrogen base; and (C) a mixture of an organic nitrogen base and an acid selected from the group con- [56] References Cited sisting of sulfuric acid, sulfurous acid and sulfamic acid, and

heat treating the product in an inert atmosphere at a tempera- UNITED STATES A N ture of at least about 400 C. for a period of time sufficient to bring about carbonization. 3,305,315 2/1967 Bacon et al ..23/209.4 3,297,405 1/1967 Sperk et al ..23/209.4 6 Claims, 8 Drawing Figures 2'60 3&0 320 380 HEAT TREflTME/VT TEMPERATURE (C) PATENTED FEB H972 3.639140 sum 2 0F 6 TENS/LE sr/wvam (Kg 25cm 0F w/arm A 0 I fi HEAT TREATMENT TEMPERATURE ("C PROCESS FOR CARBONIZED ClElLlLlUlLOSlE FlllBlElR OR THE PRODUCTS THlERlEUF The present invention relates to a process for producing excellent carbonized fiber or the product thereof by treating cellulose fiber or the product thereof with a specific strength increasing agent or a treating agent prepared by adding a flame resistance improving agent to said strength increasingagent and thereafter heat-treating the thus treated cellulose fiber or product thereofin an inert atmosphere. More particularly, the present invention concerns a process for carbonizing cellulose fiber or the product thereof characterized by treating cellulose fiber or the product thereof with a strength increasing agent obtained by the combination of sulfur-containing acid and nitrogen-containing base or with a treating agent obtained by adding a flame resistance improving agent to said strength increasing agent, thereafter carbonizing said cellulose fiber or product thereof by the heat treatment at a temperature of up to about 1,000 C. in an inert atmosphere and further if necessary carbonizing or graphitizing the thus heat-treated fiber or product thereof by the heat treatment at a temperature of about 1,000 C. or higher in an inert atmosphere.

A process for producing carbon fiber or graphite filament using cellulose fiber as a starting material has been known for a long time. Thomas Edison presented in US. Pat. No. 223,898 (1880) a process for preparing carbon fiber by dissolving cotton or flax in a zinc chloride solution, extruding this solution in an alcohol coagulating bath to obtain a fiber and heattreating the thus obtained fiber. Further, W. R. Whitrey showed in U.S. Pat. No. 916,905 (1909) a process for graphitizing carbon fiber by the heat treatment at a temperature of 2,300 C. or higher.

However, these actually produced in these days possess such defects as weak mechanical properties and too large porosity ratio so that the loss due to oxidation was large. The reasons for such defects are the facts that, in the case of pyrolyzing cellulose, the deterioration suddenly occurs par ticularly in the temperature range of 200 to 260 C. and the decomposition accompanying the gas generation suddenly occurs in a temperature range of 260 to 500 C. Therefore, if the heating rate is high, the degree of deterioration become high and the mechanical properties are reduced. Thus those having past through such a stage, even if heated at a further high temperature do not afford high-quality carbon fiber or graphite filament.

By such reasons, a process for preventing the deterioration by heating cellulose fiber at an extremely low heating rate has been proposed. British Pat. No. 1,025,499 (1964), for example, employ the heating within a temperature of from 150 to 540 C. at a heating rate of to 30 C./8 to 30 hours. Thus, this process requires 3 to 50 days for elevating the temperature up to 540 C. Moreover, Japanese Pat. Publication No. 131 13/61 employs the heating to 400 C. at a heating rate of 10 to 50 C./hr. and thereafter the heating to 900 C. at a heating rate of 100 C./hr. or less.

The present invention relates to a new process which improves the above-mentioned conventional processes in the production of carbonlike fiber, carbon fiber, graphite filament or products thereoffrom cellulose fiber or products thereof.

The object of the present invention is to provide a new treating agent or strength-increasing agent which prevents the deterioration of cellulose due to the pyrolysis in the heating treatment of cellulose fiber or products thereof.

Another object of the present invention is to provide a process for highly reinforced flexible carbonlike fiber, carbon fiber, graphite filament or products thereof by treating cellulose fiber or products thereof with the above-mentioned strength-increasing agent in the heating treatment of cellulose fiber or products thereof.

Further another object of the present invention is to provide a process for highly increasing the strength of the heat-treated fiber or the products thereof in the heat treatment at a temperature of 200 to 500 C. at which the deterioration of cellulose is particularly remarkable and in the heat treatment at further higher temperatures.

Further another object of the present invention is to provide an industrially extremely excellent process which enables the heat treatment of high-heating velocity in the heat treatment of cellulose fiber or the products thereofv in order to attain the above-mentioned objects, the present invention, prior to the heat treatment of cellulose fiber or the products thereof, requires the treatment with a specific strength increasing agent. This strength increasing agent is the later defined compound or a mixture prepared by the combination of sulfur-containing acid and nitrogen-containing base. The sulfur-containing acid and nitrogen-containing base herein include the following compounds.

That is, the sulfur-containing acid includes sulfuric acid (H sulfurous acid (H 80 thiosulfuric acid (Ii- 8 0 sulfamic acid (HSO NH and imidosulfonic acid ((HSOQ N H), and the nitrogen-containing base includes urea, urea derivatives, thiourea, thiourea derivatives and amines such as urea (CO(NH thiourea (CS(NH guanidine (NH:C(NH dicyandiamide (NH C:NHNHCN), dicyandiamidine (NH GNHNHCONHJ, triethylamine ((C H -,N triethanol amine ((CH CH OH H),

5 pyridine N) and aniline (-Nllz) and ammonia (NH The strength increasing agent of the present invention is a compound or a mixture prepared by combining one or more compound of the above-mentioned sulfur-containing acid with one or more compounds of the above-mentioned nitrogencontaining base, and such a strength increasing agent is classified into the following three groups depending on the combinations thereof as a matter of convenience.

1. Compounds prepared by the combination of sulfur-containing acid and ammonia, that is, ammonium salts of sulfurcontaining acids which include ammonium sulfate, ammonium bisulfate, ammonium sulfite, ammonium bisulfite, ammonium thiosulfate, ammonium sulfamate and ammonium imidosulfonate.

2. Mixtures prepared by the combination of a sulfur-containing acid, an ammonia and a nitrogen-containing base other than ammonia. That is, mixtures of an ammonium salt of sulfur-containing acids mentioned in the above paragraph (1) with urea, a urea derivative, thiourea, a thiourea derivative or an amine. For example, a strength increasing agent prepared by mixing an ammonium salt in the above-mentioned paragraph (l) with urea, thiourea, guanidine, triethanolamine or the like.

3. Strength increasing agent prepared by the combination of sulfur-containing acid and nitrogencontaining base other than ammonia. That is, a strength increasing agent prepared by the combination of a sulfur-containing acid with urea, 21 urea derivative, thiourea, a thiourea derivative or an amine. For example, sulfuric acidguanidine, sulfuric acid-ethylenediamine, sulfuric acid-dlicyandiamine or a strength increasing agent prepared by adding urea, thiourea, aniline, triethanolamine or the like to sulfuric acid, sulfurous acid or sulfamic acid.

With respect to the above-mentioned strength increasing agent, the ammonium salt of paragraph 1) may be a mixture of 2 or more members thereof, and the strength increasing agent of paragraph (2) may be prepared by adding one or more kinds of such nitrogen-containing bases as urea and the like to two or more kinds of ammonium salts. Further, the strength increasing agent of paragraph (3) may be prepared by further adding 1 or more kinds of such nitrogen-containing bases as urea and the like to such a compound as sulfuric acidguanidine, sulfuric acidethylenediarnine, etc.

In addition, with respect to the above-defined sulfur-containing acid, thiosulfuric acid and imidosulfonic acid do not exist as a single compound but only in the form of the compound of said acids combined with other compound. Accordingly, the above-mentioned strength increasing agent of paragraph (3) does not include the case of thiosulfuric acid and imidosulfonic acid being the acid component thereof.

Ammonium thiosulfate and ammonium imidosulfonate are actually existing compounds and exhibit the excellent strength increasing effect mentioned later.

With respect to the strength increasing agent of paragraph (3) sulfuric acid-guanidine and sulfuric acid-ethylenediamine as a compound are exemplified, but strength increasing agents of the other combinations seemingly form the salts thereof in an aqueous solution.

Every above-mentioned strength-increasing agent is generally used in the form of aqueous solution thereof in the treatment of cellulose fiber or the products thereof. Therefore, it seems that said strength increasing agent is impregnated in and adheres to cellulosic fibers or articles thereof in a form of a salt or a mixture of the salt and nitrogen-containing base excluding ammonia.

FIGS. are described below.

FIG. 1 shows the relationship between the strength of heattreated cloth obtained and the temperature of heat treatment, in the heat treatment of viscose rayon cloth wherein A represents the case of heat treatment in nitrogen and B, that in air;

FIG. 2, the relationship between the strength of heat-treated cloth obtained and the temperature of heat treatment, in the heat treatment of viscose rayon cloth preceedingly treated with a strength increasing agent wherein A represents the case of ammonium sulfate-diammonium hydrogen phosphate mixture system and B, the case of single ammonium sulfate system;

FIGS. 3 and 4, the relationship between the adhesion percentage of ammonium salt of sulfur-containing acid to viscose rayon cloth and the strength of the heat-treated cloth obtained in the heat treatment of viscose rayon cloth preceedingly treated with the said salt wherein A represents the case of ammonium sulfamate, B the case of ammonium sulfate, C the case of ammonium imidosulfonate, D the case of ammonium sulfite, E the case of ammonium thiosulfate and F the case of ammonium bisulfate;

FIG. 5, the relationship between the composition of the ammonium saIt-nitrogen-containing base strength increasing agent and the obtained strength of the heat-treated cloth in the heat treatment of viscose rayon cloth precedingly treated with the said strength increasing agent wherein A represents the case of ammonium sulfite-urea system, B the case of ammonium sulfite-thiourea system, C the case of ammonium bisulfate-urea system and D the case of ammonium sulfitetriethanol amine system;

FIG. 6, the relationship between the adhesion percentage of the sulfur-containing acid-nitrogen-containing base strength increasing agent and the obtained strength of heat-treated cloth in the heat treatment of the viscose rayon cloth preceedingly treated with the said strength increasing agent wherein A represents the case of sulfuric acid-urea system, B the case of sulfuric acid'guanidine, C the case of sulfuric acidthiourea system, D the case of sulfuric acid-triethanol amine system, E the case of sulfuric acid-ethylene-diamine and F the case of sulfuric acid-dicyandiamine; and

FIGS. 7 and 8, the relationship between the composition of the sulfur-containing acid-nitrogen-containing base strength increasing agent and the obtained strength of the heat-treated cloth in the heat treatment of viscose rayon cloth preceedingly treated with the said strength increasing agent wherein A represents the case of sulfuric acid-urea system, B the case of sulfuric acid-triethanolamine system, C the case of sulfuric acid-thiourea system, D the case of sulfamic acidtriethanolamine system, E the case of sulfamic acid-urea system, F the case of sulfamic acid-urea (40 percent) system and G the case ofsulfamic acid-thiourea system.

As is known, cellulose fiber, on pyrolysis, initiates its decomposition accompanying the weight loss at a temperature of about 150 to 160 C., and the strength of the fiber decreases. Particularly, in the case of pyrolyzing cellulose fiber to carbonate the same for a long period of time such as 1 hour or more, this tendency is remarkable and the strength of fiber suddenly falls at a temperature of 200 C. or higher. FIG. 1 is an example which shows this tendency, and shows the relationship between the obtained tensile strength of heattreated cloth and the temperature of heat treatment when viscose rayon diagonal cloth is heated up to the specified temperatures at a heating rate of 5 C./min. and heat-treated at each temperature for 1 hour respectively. This figure shows that the strength of viscose rayon diagonal cloth suddenly falls at a high-heat treatment temperature in both cases of heat treatment atmosphere being air and nitrogen, that an inflection point of the strength exists in the vicinity of 280 C. and the strength of said cloth does not depend on the heat treatment atmosphere.

In contrast thereto, the heat treatment of cellulose fiber soaked in the above-mentioned strength-increasing agent includes the temperature of remarkable strength reduction at a temperature of to C., but suddenly recovers the strength at a temperature of higher than 180 C. In addition, this heat treatment of such processed fiber affords flexible heat-treated fiber having high strength at a temperature of 280 C. or higher at which the heat treatment of cellulose fiber not soaked in such a strength increasing agent simply gives ex-.

tremely low strength, in other words flexible heat-treated fiber with low-strength reduction, and in this case the strength increasing action of strength increasing agent relates to the adhesion percentage or the mixing ratio of such a nitrogen-containing base urea with a sulfur-containing acid. Thus, by the above-described finding, the present invention has been completed.

In view that such strength increasing action of the strength increasing agent of the present invention cannot be obtained by such salts as ammonium nitrate, ammonium chloride, ammonium acetate, ammonium oxalate, ammonium formate, ammonium phosphorates and the like and that these salts rather reduces the strength of heat-treated fiber, it is considered that sulfur may play a main role of strength increasing action. However, the fact that aluminum ammonium sulfate, zinc ammonium sulfate, nickel ammonium sulfate or the like, which is an ammonium salt of sulfur-containing acid but contains a metal atom in the molecule, does not possess strength increasing action suggest that the compounds containing these metal atoms are not preferable.

The strength increasing action of such a strength-increasing agent, in general, increases together with the increase of the adhering amount thereof to cellulose fiber or the products thereof. Too much adhesion thereof, however, involves such secondary disadvantages as the starting material fiber or the products thereof being hardened too much resulting in the in convenience in the handling thereof or the soaking treatment becoming difficult, but the strength increasing effect is unaltered.

When ammonium salt-nitrogen-containing base system or sulfur-containing acid-nitrogen-containing base (excluding ammonia) system is used as a strength increasing agent, it is observed that the strength of heat-treated fiber or the products thereof decreases slowly or suddenly when the adhesion percentage of the strength increasing agent exceeds a certain value. With respect to such strength increasing agent, the strength increasing action thereof also depends on the mixing proportion of nitrogen-containing base with ammonium salt or sulfur-containing acid which is the acid component of said ammonium salt, and it is recognized that, with respect to every strength increasing agent, the most suitable mixing ratio or the preferable mixing ratio exists.

The strength increasing agent of the present invention having the above-mentioned strength increasing action is subsequently described concretely.

FIGS. 2 to 4, of the strength increasing agents of the present invention, show the strength increasing action of strength increasing agents obtained by the combination of sulfur-containing acid and ammonia, that is, of ammonium salts of sulfur-containing acid. FIG. 2 shows the relationships between the strength of the heat-treated cloth and the temperature of dbl b d ltl heat treatment in the cases where two pieces of viscose rayon diagonal cloth are individually soaked in aqueous solutions of two strength-increasing agents such as ammonium sulfate and ammonium sulfate containing 15 weight percent of the later tion of ammonium bisulfate, dried and allowed to stand at room temperature for 1 day or more without any further processing. In the heat treatment of cellulose fiber or the products thereof treated with ammonium bisulfate, such britdescribed flame-resistance-improving agent of diammonium 5 tle action may be involved in a series of steps of soaking, dryhydrogen phosphate, the adhesion percentage of the former ing and heat treatment, resulting in the reduction of the strength increasing agent is 41.6 percent and that of the latter strength of starting material fiber or the products thereof. is 44.8 percent (which is the total adhesion ratio of ammoni- After all, the highly strong heat-treated fiber or the products um sulfate and diammonium hydrogen phosphate) and both thereof may not be obtained. soaked pieces of cloth are individually heattreated in nitrogen nc am bisulfite Contains asidic H in its molecule. atmosphere for 1 hour. It is recognizable from FIG. 2 that if it shows the same behavior as ammonium bisulfate and has cellulose is treated with ammonium sulfate, the decomposition subst ly the e eng eas g on as oniof cellulose initiates at a temperature relatively lower than klff that of the case of cellulose being nontreated and that the The strength increasing action of ammonium sa|t-nitrogenstrength of heat-treated cloth extremely decreases within a containing base (excluding ammonia)system strength increastemperature range of 160 to 180 C. However, when the teming agent in the heat treatment in air is described below. perature of heat treatment exceeds 180 C., the strength of Firstly, the relationship between the adhesion percentage of heat-treated cloth is recovered to a large extent and the heat such a strength increasing agent to cellulose fiber or the treatment at a temperature of above 200 C. affords the exproduct thereof and the obtained strength of heat-treated tremely large strength. Such a decomposition behavior of celfiber or the products thereofis mentioned. lulose as above is also obtained in the same way in the case of Table I shows the results when viscose rayon diagonal cloth pyrolysis of cellulose treated with other strength increasing (thickness: 0.5 mm.) is treated with strength-increasing agents agent. in contrast, as is clear from FIG. ll, the pyrolysis of celof ammonium imidosulfonate and ammonium imidosulfonatelulose nontreated with a strength increasing agent excludes urea (weight ratio; 2:1) system, and heattreated in air at 250 such a phenomenon, the strength simply decreases in the tem- C. for 2 hours and further at 300 C. for 2 hours. The results in perature range measured, and the heat treatment at a temthis table shows that, in the case of single employment of am perature of above 200 C. where the heat treatment of the monium imidosulfonate, the strength oil heat-treated cloth inpresent invention gives the high strength, simply affords the creases together with the increase of the adhesion amount. In low strength. contrast thereto, in the case of ammonium imidosulfonate- FIGS. 3 and 4, when viscose rayon diagonal cloth is soaked urea system, although the strength increases together with the in each aqueous solution of ammonium sulfate, ammonium increase ofadhesion percentage, the proportion ofincrease of sulfamate, ammonium imidosulfonate, ammonium bisulfate, strength is higher than the case of single ammonium imidosulammonium sulfite and ammonium thiosulfate, and thereafter fonate. Mixture system may rather reduce the strength of heattreated in air at 250 for 2 hours and further at 300 C. for heat-treated fiber when the adhesion amount becomes large. 1 hour, show the relationship between the adhesion percent- Such a phenomenon as the strength decreasing at a high adage of each ammonium salt to the starting material diagonal hesion is also recognized in other ammonium salt-nitrogencloth and the strength of heat-treated cloth. This figure, excontaining system or the later mentioned sulfur-containing cluding the case of ammonium bisulfate, shows that the acid-nitrogen-containing base system strength increasing strength of heat'treated cloth increases in accordance with the 40 agent, and may be a general phenomenon of such cases.

TABLE 1 Adhesion percentage (por- 0 6.4 13.7 20.1) 33.2 52. ll 70.2 Ammonium cent;

imidosul- {Tensile strength (kg/2.5 2.7-3.1 (1.0 8.1 12.1 12. 0 15.8 10.1 Ionate. 0111.). Ammonium Adhesion percentage (per- 0 22.7 37. 6 42.5 51.7 66.3 78.15

imidosulcent). fonate {Tensile strength (kg/2.5 2.7-3.1 12.5 15.7 17.2 1 1.3 7.1) 2.2 urea. cm.).

increase of adhesion percentage of ammonium salt.

In the case of ammonium bisulfate, when the adhesion percentage is higher than about 10 percent, the strength of heat treated cloth decreases. Therefore, in the case of using ammonium bisulfate, the soaking treatment should be carried out so as to give about 10 percent of adhesion percentage. It is considered that such behavior of ammonium bisulfate is due to its brittle action against cellulose the action of acidic H existing in the molecule of ammonium bisulfate. For example,

he t-teste Cloth. is issribs Tables 2 and 3 show the results when viscose rayon diagonal cloth is treated with strength increasing agent prepared by mixing urea, thiourea or triethanol amine with ammonium sulfate, ammonium sulfamate or ammonium imidosulfonate and thereafter heattreated in air at 250 C. for 2 hours and viscose rayon cloth tnolders if it is soaked in an aqueous solu further at 300C. for 2 hours.

TABLE 2 '1ruatn1autwlth strength increasing agent Hoot-treated cloth 'lonsllo Adhesion strength percentage (longilotul (percent) of Adhesion lloutlug tlullnal) lllnuuutlon tulhnslon umtnonlum percentage wolght (kg/2.6 Gourd Mixing ratio of basin to percentage lznidoof baso loss um. 01' tutllllnl) mnluonlum salt (wright. ratio) (percent) sultonnto (percent) (percent) width) (percent) N oil-treated -70 2. 7--3. 1 5. 2-5. ti Ammonium imld ulfouattuuroa:

:0 25.5 25.5 0 63 11.7 11.0 82. 7 25. '2 6. 5 61 11. 2 11. 6 37. 6 25.1 12. 5 5'2 15. 7 12.1) [30. 0 20.1 21. S 65 12. I 10.4 64. 0 32. 0 32. 0 55 10. 8 I0. I)

'IABLF. 2-- Continued Heat-treated cloth Tunsllo Adlmslon strength percentage (longilu1.ul (percent) of Adhesion Hunting iudlmil l'llon 'utlon adhesion ammonium percentage weight. (kg/2.5 longi- Mixing ratio of base to percentage imidoof base loss cm. of tudiunl) am in onlum salt (weight ratio) (percent) sullonnto (percent) (percent) width) (percent) Ammonium imldo5ul10natc:thi0- M urea:

100: 2 2 28.7 28.7 63 lLh 115. 100:25 35.3 28.2 7.1 53 11.8 10.0 100: 50 42. 28. 3 14. 2 50 15. 0 1 .0 100: 75 52. 2 29. 8 22. 4 411 11. 5 S. 3 100:100 68. 0 34. 4 34. 5 4e 10. o 11.0 Ammonium imidosulionate: tricthanolamino:

TABLE 3 Treatment with strength increasing agent Heat-treated cloth Tensile Adhesion strength Total per- Adhesion (longi- Elonadhesion eentage of percent- Heating tudinal) gation perammonium age of weight (kg/2.5 (longi- Mixing ratio of base to centage s t base loss cm. of tudinal) ammonium salt (weight ratio) (percent) (percent) (percent) (percent) width) (percent) Non-treated 75-76 2. 7-3. 1 5. 2-5. G Ammonium sulfatezurea:

The results in Tables 2 and 3 show that, in the case of using Ammonium bisulfate-urca system singly ammonium sulfate, ammonium sulfamate or ammonium imidosulfonate, the strength of heat-treated cloth increases by about three times as much as the strength of heat-treated cloth obtained from the nontreated starting material cloth. in the cases of adding urea, thiourea or triethanolamine to the above-mentioned ammonium salts, the strength increasing action in every case is larger than that of the corresponding case of single ammonium salt employment. At a suitable mixing ratio, the strength of heat-treated cloth increases by four times or more as much as that of the case without such a treatment, and decreases via the maximum value when the mixing ratio is changed.

FIG. 5 shows the cases of mixing urea, thiourea or triethanolamine with ammonium sulfite and mixing urea with ammonium bisulfate. FIG. 5, when viscose diagonal cloth is soaked in each aqueous solution of the above-mentioned strength increasing agents so as to produce almost constant adhesion percentage of ammonium salt and to vary the adhesion ratio of the nitrogen-containing base, wrung, dried, and thereafter heattreated in air at 250 C. for 2 hours and further at 300 C. for 1 hour, shows the relationship between the strength of heat-treated cloth and the composition of each strength increasing agent. Provided that, in the said heat treatment, the adhesion percentages of ammonium salt to the starting material cloth, with respect to each strength-increasing agent, are as follows:

adhesion percentage of ammonium sulfite adhesion percentage of ammonium sulfitc Ammonium sulfite-ureu system Ammonium sulfite-lhiourea system adhesion percentage of ammonium bisulfate As is clear from FIG. 5, the above-mentioned systems of the combination of an ammonium salt and a base also differ from each other in their strength increasing action, but all of these exhibit strength increasing action. In addition, the effect of such a base as urea or the like on the strength increasing action of ammonium salt is clearly recognizable. That is, the strength increasing action of these systems relates to the mixing proportion thereof. With respect to the system of ammonium salt and urea or thiourea, as the proportion of base increases the strength increasing action thereof is strengthened. When the molar ratio of base to ammonium salt is from 0.75 to 1.00, a peak of strength increasing action is obtained. and the strength increasing agent of this molar ratio gives high strength to heat-treated cloth by 4 to 7 kg. higher than the case of using singly ammonium salt.

With respect to ammonium sulfite-triethanolamine system, when the mixing ratio of triethanolamine is 1.00 or higher by molar ratio, the effect of base which promotes the strength increasing action of ammonium sulfite appears.

it is noteworthy that, as is clear from FIG. 4, the strength increasing action of ammonium bisulfate, which is weaker than that of ammonium sulfite, ammonium thiosulfate or the like is extremely strengthened by the addition of base to said ammonium bisulfate so as to give the strength-increasing action which is comparable to the strength increasing action of ammonium sulfite, ammonium thiosulfate or the combinations of these ammonium salts with a base. This is because that acidic H in an ammonium bisulfate molecule, which seemingly exerts deterioration or brittle action to cellulose fiber materials, is neutralized by such a base as urea or the like to form the salt thereof, therefore, the thus produced salt behaves in the same way as such a neutral salt as ammonium sulfite or the like. and,

in addition, the effect of base obtained when such a base as urea is added to such a neutral salt as ammonium sulfite, ammonium thiosulfate or the like is exhibited.

in the case of adding such a base as urea or the like to ammonium bisulfite which contains acidic H in its molecule as 5 ammonium bisulfate does and simply exerts strengthincreasing action comparable to that of ammonium bisulfate, almost identical strength increasing action can be obtained.

in the ease of using ammonium thiosulfate as the ammonium salt, the effect of base almost identical with that of the cases of other ammonium salt can be obtained as well. The case of ammonium thiosulfate-base system is to be described in examples below.

With respect to the above-mentioned ammonium salt-base strength increasing agents, the most effective base, when combined with ammonium salt, is urea and thiourea. Triethanolamine, guanidine and triethylamine, in this case, belong to a second class as the compound exerting the base effect. Dicyandiamide, dicyandiarnidine, aniline, pyridine and the like belong to the group of compounds exerting relatively low base effect.

Subsequently, the strength increasing action of the system comprising a sulfui'containing acid and a nitrogen-containing base other than ammonia is described. H6. 6, when viscose rayon diagonal cloth is soaked in a respective aqueous solution of sulfuric acid-urea system (molar ratio; 1:2.75), sulfuric aeid-thiourea system (molar ratio; l:l sulfuric acidtriethanolamine system (molar ratio; 1:3), sulfuric acid-guanidine ([hll-l:C(Nll-I 'H SO,, acid-ethylenediamine ((NH CH Cl-I NH 'l i fiO and sulfuric aeid-dicyandiamidine ((NH CShlllllHCOhll-l,) zli Sfly 21-1 0), wrung, dried and thereafter heat-treated in air at 250? C. for 2 hours and further at 300 C. for 1 hour, shows the relationship between the adhesion percentage ofeach strength 35 increasing agent and the strength of heattreated cloth. FIG. 7, when viscose rayon diagonal cloth is soaked in each aqueous solution of sulfuric acid-urea system, sulfuric acid-thiourea system and sulfuric acid-triethanolamine system strength in creasing agents so that the adhesion percentages of sulfuric 4O acid, which are the acid component of the said strength increasing agents, are almost constant such as 15.0 percent, 1 L3 percent and 5.9 percent, respectively, and so that the adhesion percentages of base components thereof are varied, and thereafter heattreated in the same manner as above, shows the relationship between the mixing ratio of each strength increasing agent and the strength of heat-treated cloth.

FIG. 8 shows the case of sulfamic acid base system. MG. 8 when viscose rayon diagonal cloth is soaked in an aqueous solution of respective strength increasing agent prepared by mixing urea, thiourca or triethanolamine with sulfamic acid at respective suitable mixing ratio and subsequently heat-treated in air at 250 for 2 hours and further at 300 C. for 1 hour, 55

sulfuric min adhesion percentage of sulfamic acid almost constant (about 20 percent) and the adhesion percentage of base varied. With respect to sulfamic acid-urea system, the case where the adhesion percentage of sulfamic acid is about 40 percent is also shown. In the figure, F represents this case.

The above-mentioned FIGS. 6 to it show the fact that, in the case of such strength increasing agents, the strength of heattreated cloth also relates to the adhesion percentage of strength increasing agent and to the composition thereof, as in the case of the aforesaid single ammonium salt system or ammonium salt-nitrogen-containing base system.

That is, with respect to the relationship between the adhesion percentage and the strength, H6. 6 shows that the strength of heat-treated cloth increases in harmony with the increase of adhesion percentage of strength increasing agent and that, when the adhesion percentage exceeds a certain value, the strength gradually or suddenly decreases. ln the case of sulfamic acid-urea system, FIG. ti shows that, within a certain mixing range, sulfamic acid with 40 percent adhesion percentage exerts stronger strength increasing action than that with 20 percent aehesion percentage.

Moreover, with respect to the relationship between the composition of strength increasing agent the strength, FIGS. "7 and 8 show that, with respect to every strength increasing agent, the most suitable or preferably mixing ratio exists.

The strength increasing agent of sulfurous acid-base system behaves in the same way as that of sulfuric acid-base system and exerts almost identical strength increasing action. This is described in examples below.

in FlG. ti, when base is not added at all, but when sulfamic acid is singly used, the strength of heat-treated cloth is small. This fact is seemingly because that sulfamic acid may deteriorate the starting material cloth during the sulfamie acid soaking step or a series of steps after the said soaking step.

With respect to the strength increasing agents of sulfur-eontaining acid-nitrogen-containing base (excluding ammonia) system, if urea, thiourea, guanidine, triethanolamine or the like as a nitrogen-containing base is combined with a sulfurcontaining acid, extremely or relatively strong strength increasing action can be exerted. in contrast thereto, dicyandiamide, dicyandiamidine, triethylamine, aniline, pyridine or the like belongs to a compound which exerts relatively weak strength increasing action.

The strength increasing agents described in detail above exert strength increasing action even if the heating atmosphere is changed from air to an inert. atmosphere. Further,

the effectiveness of said action is also almost identical. Table 4 is an example which shows this fact, and shows the results when viscose rayon diagonal cloth is treated with an aqueous solution of treating agent of ammonium imidosulfonate and urea with a weight ratio of 2:1 so as to make the adhesion percentage thereof4i.l percent and thereafter heattreated in air and in nitrogen which is an inert atmosphere. in addition, for comparison, the case where the nontreated viscose rayon diagonal cloth is heattreated under the identical conditions is ,9 sho nrtlivn rtli inert-rising agent of respective mixing ratio to the "table 4 shows the fact that, in this case, even i! the at- .slartlup umtrriul diagonal cloth is controlled so in: to main: the mosphcre of heat treatment is air or nitrogen, almost similar ill.

strength increasing actions are exerted. Other strength in creasing agents of the present invention act in the same way as the above-mentioned strength increasing agent of ammonium imidosulfonate-urea system. This fact is clarified by examples below. The influence of the atmosphere at heat treatment is described a little additionally. ln the heat treatment at such a high temperature as l,000 C., for example, the heat treatment in an inert atmosphere affords the stronger strength to heat-treated cloth than that in an oxidative atmosphere.

As an inert gas, helium, argon, carbon dioxide or the like may be used, in addition to nitrogen.

The present inventors, by heat-treating cellulose fiber or the products thereof, precedingly treated with a kind of strength increasing agents, in air within a temperature range of 200 to 350 C. and then further heattreating the thus heat-treated fiber or the products thereof in an inert atmosphere at a temperature of up to about 1,000 C., have succeeded in the production of stronger carbonlike fiber or the products thereof than the heat-treated substances under the same conditions of nontreated cellulose fiber. This process, however, requires the heat-treatment for a long period of time, for example, 2 hours at 250 C. andfurther l to lioggs at 300 C., in order to avoid the rapid oxidative combustion in the heat treatment at a temperature of 200 to 350 C. in air and to obtain the high strength of heat-treated substances, and thus requires total 3 to 4 hours as the heat treatment time. A process employing the heat treatment in an inert atmosphere after the heat treatment in air as in the above-mentioned manner requires two types of furnaces or two steps of heat treatment, and is not an industrial satisfactory process although this process affords highly strong carbonlike fiber or the products thereof and highly efficiently produces the same as compared with the conventional technique for the production of carbonlike fiber.

In contrast thereto, the process for carbonizing cellulose fiber or the products thereof of the present invention wherein cellulose fiber or the products thereof are treated with a kind of the above-mentioned strength increasing agents, thereafter the thus treated fiber or the products thereof are converted to carbonlike substances by the heat treatment at a temperature of up to about l,000 C. in an inert atmosphere and if necessary, the thus heat-treated fiber or the products thereof are carbonized or graphitized by the further heat treatment at a temperature of higher than about 1,000 C. in an inert atmosphere, as is clear from examples shown below, enables the production of highly strong carbonlikc fiber, and further excellent carbon fiber, graphite fiber or the products thereof by the heat treatment with such a high heating rate as l to 5 C./1nin. over the temperature range offrom room temperature to l,000 C., and does not require two types of'furnaces or two steps of heat treatment. Thus, this process is an industrially extremely advantageous process. I

In view the fact that the treated substance with a strength increasing agent of the present invention, even when heated at any heating rate, always exerts higher strength and results in higher yield than the nontreated substance, when the two are compared at the same heating rate it is self-evident that the heating rate of the said treated substance is not necessarily limited within the above-mentioned heating rate. In general, since heat treatment at a lower heating rate results in heattreated fiber or articles thereof having higher strength, it is natural that not only this invention is restricted to said heating rate, but also this invention includes the case of heat treatment at a heating rate of less than l C./min.

Carbon fiber or graphite fiber with a carbon content of about 95 percent or above can be produced by heattreating the carbonlikc fiber prepared according to the above-mew tioned process of the present invention (carbon content: up to about 90 percent) at a temperature of higher than about l,()00 C. according to the conventional process. Even in this case, however, if the highly strong carbonlike fiber produced by the process of the present invention is used as the starting material, the stronger carbon fiber or graphite fiber than the conventional carbon or graphite fiber can evidently be ob tained.

in case the present invention is applied for the industrial large-scale heat treatment, air incorporated in the heat treatment furnace, air initially contained in the cloth or oxygen contained in an inert gas may cause the deterioration of heattreated fiber or the products thereof due to the oxidation by said air or oxygen. Such a heat treatment may often afford the lower strength to the heat-treated fiber or the products thereof than the experimental heat treatment where the heat treatment atmosphere is completely replaced by an inert gas, in order to avoid this disadvantage, the starting material fiber or the products thereof may be soak-treated with a strength increasing agent, to which is precedingly added such a compound as ammonium phosphates, guanidine phosphate, aluminum ammonium sulfate, tetrakis hydroxymethyl phosphonium chloride (THPC) and the like, which is called as a flameresistance-improving agent clarified in the present inventors invention relating to the process for the production of flameresistant fiber.

That is, as is clear from table 5, the soak treatment of the starting material cellulose fiber or the products thereof with an aqueous solution of the above-mentioned compound called as a flame-resistance-improving agent, even if the thus soaked fiber or the products thereof are heated treated in air, affords the heat-treated fiber or the products thereof which do not involve not only the combustion but also the ember combustion and the reduction to ashes, in other words, the heat-treated fiber or the products thereof excellent in oxidation resistance. Accordingly, if the present invention is applied after treating cellulose fiber or the products thereof with a treating agent prepared by adding the above-mentioned flame-resistance-improving agent to a strength increasing agent of the present invention having been described in detail, even if oxygen is contained in an inert atmosphere, the heat-treated fiber or the products thereof excellent in oxidation resistance due to the presence of flame-resistance-improving agent can be produced, and thereby the oxidative deterioration due to said oxygen or air contained in the starting material fiber or the products thereof may be inhibited so as to give preferable results.

Table 5 shows the results of the cases where diammonium hydrogen phosphate, triammonium phosphate, guanidine phosphate, THPC and aluminum ammonium sulfate are employed as a flame-resistance-improving agent. The case of ammonium dihydrogen phosphate also exerts the identical action. In this case, two kinds or more of flame resistance improving agents may simultaneously be used, and the amount of addition thereof may be small as compared with that of strength increasing agent.

TABLE 5 Flame resistance improving agent Heat-treated cloth Tensile strength Adhesion (longiper- Weight tudmal) Flame centage, loss, kg./2.5 cm. resist- Kind percent percent of width enco 0 78 5.8 C None a 59 4.2 1; Diarnmonium hydrogen i6 52 3. I

t 24 48 2.2 A phospha e 32 38 1.5 A 8 59 it Triammonium hos- 16 53 phate. p 24 46 2.) A 32 40 2 6B Guanidine phosphate G2 A i 8 69 2.6 A THPC "i 16 51 as i luminum ammonium 8 68 i sulfate. i 16 62 0.2 A

NorE.-Startin material cloth: viscose rayon diagonal cloth conditions of heat trcatmonti 250 C. l hour plus 300 C. 2 hours (in air):

A=not burning into i]. flame; no umber combustion; no reduction to ashes. B=not burning into a llama; no ember combustion; reducing to mates. 7 i 1 (i=n0t burning into n. Home; umber-burning; rrnluclng 0 its 105.

Ill?) The condition of heat treatment of the present invention should suitably be determined depending on the texture, shape, etc., of the starting material fiber or the products thereof. For example, when a big rattan, thick woven stuff, thick nonwoven cloth or felting is heattreated, heat generated by the pyrolysis thereof is liable to be stored up inside the texture thereof, and thereby the abnormal heat generation is involved so that the temperature controlling may sometimes become difficult. In this case, such a method as reducing the heating rate should be applied.

The properties concerning the strength of heat-treated fiber or the products thereof obtained by the present invention, as mentioned above, depend on the kind of strength increasing agents, the adhesion percentage thereof, mixing ratio thereof, heat treatment conditions and so on, and in addition thereto, relates to the microstructure of starting material cellulose. That is, generally, the higher the degree of orientation ofstarting material cellulose, the larger the strength of the heattreated fiber or the products thereof and the smaller the elongation thereof. The heat-treated fiber of such a highly crystal-- line cellulose fiber as polynosic fiber, cotton or the like is generally brittle, but such brittleness can be avoided if such crystalline starting material fiber is precedingly treated according to such a known method as mercerization or the like to reduce the degree of crystallization thereof and then heattreated.

Of the present invention, the starting material fiber or the products thereof are not limited within the fiber or the products thereof singly comprising cellulose fiber, but include the fiber or the products thereof which is prepared by mixing such a known fiber able to be carbonated by pyrolysis as polyacrylonitrile fiber, polyvinylalcohol fiber or the like with cellulose fiber. Of the present invention, cellulose fiber includes not only the fiber singly comprising cellulose fiber but also all of the fibers composed of the every above-mentioned materials, and represents every kind of the above-mentioned fibers.

As is described in detail above, the present invention, in the production of carbonlike fiber, carbon fiber, graphite fiber or the products thereof from cellulose fiber, enables the preparation of carbonlike fiber or the products thereof having the strength several times higher than the case ofusing nontreated cellulose fiber as a starting material even at a temperature of 200 to 500 C. which belongs to the most dangerous temperature range wherein the mechanical properties of the carbonated fiber may be deteriorated, by precedingly treating cellulose fiber or the products thereof with a strength increasing agent provided for in the present invention or a treating agent prepared by adding a flame resistance improving agent to said strength increasing agent, and subsequently by heattreating the thus treated fiber or the products thereof at a temperature of up to about 1,000 C. in an inert atmosphere, and thereby, enables the highly efficient production of carbon fiber, graphite fiber or the products thereof having the further higher strength than that of the conventional art, by the heat treatment of carbonation or graphitization at further higher temperature.

The present invention is further described below in accordance with examples, but the present invention naturally is not limited by these examples.

EXAMPLE 1 By soaking viscose method cellulose fiber (5.5 d; tensile strength (dry): 10.7 g.; tensile tenacity (dry): 1.9 g./d; elongation: 21.3 percent) in an aqueous solution of ammonium sulfate with a concentration of 400 g./l., wringing the thus soaked fiber with a wringing percentage of 100 percent and drying the wrung fiber at [20 C. for l5 minutes, cellulose fiber having the adhesion percentage of ammonium sulfate of 40 percent was prepared. Thereafter, said cellulose fiber and nontreated cellulose fiber were individually placed in a respective sealed container replaced by nitrogen and heattrcated by elevating the temperature, at a heating rate of 5 C/min. to 400 and 600 C. respectively.

ll All Meanwhile, by heating the above-mentioned cellulose fiber in air at 250 C. for 2 hours and further at 300 for 1 hour, the heat-treated fiber in air was prepared, and further the thus heat-treated fiber was placed in a sealed container replaced by nitrogen and heated at a heating rate of 5 C./min. to 400 and 600 C., respectively.

The following table shows the thus obtained results, wherein A represents the heat-treated fiber obtained by directly heating the treated cellulose fiber in nitrogen; B represents the heat-treated fiber obtained by heattreating the nontreated cellulose fiber in the same manner as A; and C represents the heat-treated fiber obtained by heating the treated cellulose fiber in air and thereafter in nitrogen. That is, A is prepared by the process of the present invention; B, by the conventional method; and C, by other process of the present inventors in- Men o -,7

Elongation (dry) 3.23 4.60 5.20 1.53 1.17

in comparing A with B, A has about 40 percent higher yield than B and the tensile strength of A is -4 to 9 times higher than that of B. Subsequently, in comparing A with C, this measu rement shows that the tensile strength of C is 15 to 25 percent higher than that of A. However, if the fact that A is four to nine times stronger than B is taken into consideration, it can be deduced that A and C have almost comparable strength.

Meanwhile, in comparing the heat treatment time ofA with that of C, in order to attain 600 C., A merely requires 2 hours but C requires total 4 hours (3 hours in air plus 1 hour in nitrogen). That is, it can be deduced that A is a far more highly efficient process than C.

EXAMPLE 2 Two pieces of diagonal cloth comprising viscose rayon l .5 d.) spun yarn (thread density: longitudinal, 36 threads/2.5 cm. of width, transverse, 36 threads/2.5 cm. of width; weight: 280 g./m. were respectively soaked in (A) an aqueous solution of ammonium sulfate (concentration: 400 g./l.) and in (B) a mixed aqueous solution of ammonium sulfate (concentration: 400 g./l.) and diammonium hydrogen phosphate (concentration: 70 g./l.), the thus soaked two pieces of diagonal cloth were wrung at a wringing percentage of 100 percent and subsequently dried at C. so as to obtain two kinds of treated cloth wherein the adhesion percentage of solid content of (A) was 41.6 percent and that of(B) was 44.8 percent, respectively. Subsequently, these two kinds of treated cloth were individually charged in a stainless steel cylinder equipping a nitrogen charging inlet and an opening connected with a vacuum pump and the air in the cylinder was replaced by nitrogen by the several times repeated evacuation and nitrogen introduction. Thereafter the cloth in the cylinder was heated at a heating rate of 5 C./rnin. to the desired temperature, heattreated at the said temperature for 1 hour, and then cooled down to normal temperature, and the heat-treated sample was taken out. After washing and drying, the thus heattreated samples was examined with respect to their weight loss, shrinking percentage, tensile strength and elementary analysis. For comparison, nontreated cloth was also heattreated in the same way as above, and this is represented by (C).

The obtained results are shown in the following tables. As compared with nontreated cloth (C), the heat-treated cloth obtained by the heat treatment of diagonal cloth soaked in ammonium sulfate solution (A) exhibits higher strength at any temperature and possesses both low weight loss and shrinking percentage, and thus yield thereof is high. In comparing single ammonium sulfate system (A) with ammonium sulfatc dlann monium hydrogen phosphate mixture system. the mixture system (B) affords lower weight loss and higher yield than single system (A).

IIEA'I TREATMENT 01* AMMONIUM S11 IN NITROGEN Diagonal cloth comprising viscose lvlmtsuronwnt 'lnnsllu Hhrlnkstt'nngih lug [)11t' (longlunnlngo 11111111111) 'lrnn- Wulghl. (longlhuh/2.5 lfiloinnulnry ltllltlYHlH pvrnloss turllnnl) (.lll. o) Ash, turn 1 pvrnnnl. [)1111511111. M11111 (1 ll 1) N 1 pnrcnn l. 121), (1.1) 11.11 37. 1 43.1 11. 34 411.112 1) 1) 1). 11 141). 1). 7 11.8 27.11 43. (111 11.34 41). 51 1) 11.17 11.42 1111) 12. 15.14 5. i) 42. 711 11. 01) 47.111) 11.113 0.1) 1. 93 1111). 11). 5 111. 7 4. 5 42.1111 11.1111 47. 214 11. 71) l. 111 2.114 2()0 211. 7 5.4 111. 7 511.23 4.121 211. 12 It. 74 3. ()2 0.1111 221). 25. l 4. 7 17. 2 511.014 4.27 27. H1) 11. 2. 84 1). 87 241) 28. 1 (1. 1) 17.1% 61). 152 4. 24 25.1)11 7. 32 2. 27 1). 3!) 251).. 31. 2 7. 2 15.11 111.118 4. ()8 24. 111) 7. 2H 2. ()1) 0. 27 2110 32. 8 7. 4 15. 11 (11). 74 4. 12 25. 411 7. 11 2. 111 1). 31) 281). 36. 7 1'1. 4 14. 1) 114.118 3.117 22. 31 7. 71 l. 27 (l. 28 3011.. 3.). 7 11). 1) 111. 3 115. 41) 3.112 22. 12 7. 011 1. O3 0. 311 321)... 41.11 111. 11 14. 4 57.1111 3. H1 11). 71) 7. 71 1). 77 1). 23 3011.. 43. 11 11. 5 14.2 71). 41) 8.117 17. 34 7. 57 1). 611 1). 34 401), 411.11 13.1) 12. 1 72. 42 3.111) 15. 21) 7. 711 0.51) 1). 43 5111).. 54.11 18. 2 l1). 1) 77. 84 3. ()1 11). 43 7. [)1) 1). 43 1). 31) 1i1l1) 58. 4 21). l 7. 4 82. O4 2. 54 7. 12 7.1111 1). 21 1). 21 800 113. 4 26. 5 11.11 88.1.11 1. 44 3.111) 4. (l3 1). 113 1). 35 1,001). 71). 3 27.11 0.11 111.11) 1. 11) 5.1111 1. 44 11.114 1). 27 38.11 10.7 11 5 117.13 :1. 110 10.111) 11.57 11. 1111 0.1111 .a

1 01 heat. treatment, C.

" Conditions of heat treatment 250 C. X 2 hours plus 300 llEAl TREATMENT 1N NITROGEN or oLoTn TnuATun monofilament: 1.5

wiTn MIXTURE SYSTEM '1 "lompcraturo 1 ()fhcui;11111111110111, Conditions 011111111. l.rr .ntnn'n1.250 (,1. X 2 hours plus 300 (J. X l 110111 (in nitrogen).

EATING AGENI (l1) G. X 1 hour (in nitrogen).

36 threads/2.5 cm.

EXAMPLE .1

rayon (denier o1 d) spun yarn (thread density: longitudinal, of width, transverse, 36 threads/2.5 cm. of

Measurement width; weight: 280 g./m. was soaked in an aqueous solution of each strength increasing agent, and the thus soaked cloth strength was wrung at a wringing percentage of 100 percent and subsequently dried at 80 C. for hours. Subsequently the thus Weight (longlken/2.5 treated cloth was charged m a stainless steel cylinder I mi equipping a nitrogen-charging inlet and an opening connected with a vacuum pump, and the an in the cylinder was replaced 12 &3 by nitrogen by the several times repeated evacuation and 3.1 nitrogen introduction. Thereafter the cloth in the cylinder was 5 6" :5 heated at a heating rate of 5 C./m1n. up to 500 C. and to 211.11 7.2 111.5 1,000 C., and heattreated at t e said temperatures for 1 hour. For comparison. nontreated cloth was also heattreated 1n the 33.1 11.1) 111.7 same way as above The obtained results are shown in the following table These results show that the cloth treated with 311:2 11:11 1 112 0' such a strength increasing agent gives higher strength and higher yield than the cloth which is not treated with such a 18:5 10:11 11.5 strength increasing agent. 52.1 18.3 11.0 {.11- ,1 32".; 3'? EXAMPLE 4 121-5 The same starting material diagonal cloth as in example 3 HEAT 'lltEAIMENl 1N NITROGEN O1 NON-TREATED CLOTH Sizntingvloth. I20.

Mmrsnruinunl.

Sin-inking 'lonslln porstrength uontugn (longh Wolghl (longl- Ludlnal) lfilonwninry nnnlysls-- loss, tutllnal) kg./2.6on1. Ash. percent pot'tcnl. o1 wld 1.11 11 1) pnruunI.

. 55. 4 43. 12 11. 53 511. 15 0. 21) 1). 4 0.1) 55. 1 43. 33 11. 511 41). 81) 1]. 22 1). 7 (l. 7 511.1) 43. 21) 1). 57 41). 111 1). .23 1). 7 1). 7 511. 2 43. 33 0. 68 41). 73 1). 31 1. 1 11.1) 54.1) 43. 72 11.113 41). 51) 11. 21 1.11 1. 4 54. 4 43.115 11. 57 48. 111) 1]. 211 3. 5 1). 7 41.1 44. 411 11. 48. 1113 1). 311 4. 1 (1.1) 37. 3 44. 511 11.113 411. 41 1). 15 4.1) 1). 7 11. 5 411. 37 11. 41) 411. 41 1 73 23. 2 1. 3 ll. 8 48. 41) 11.41 44. 711 1). 31 118. (i 16. 2 l1. 2 71. 03 5. 4O 22. 13B 0. 8.) 75. 4 15). 1) l). 3 71. 58 5.14 22.15 1.13 110. 2 23. 0 1). 8 76. 115 4. 82 17. O0 1. 23 80. 1 25. 1) 6. 7 76. 00 4. 56 18. 37 1. 07 83. 3 26. 2 (l. 1) 86. 35 3. 78 8. 27 1. 61) 84. 1 32. 1) (l. 4 92. 25 2.112 3. 67 1. 113 85. 3 34. 5 1). 5 H4. (14 1. 61 "X 43 1. 32 85. 3 32. O 0. 6 94. 111 1. 21) 1. 32 1. 35 BR. 4 33. 3 3. 2 9G. 11 1). 63 1. 67 2. 10 74. 5 17. 0 10.1 71.111 5. .30 1.2.111 0. 71

was soaked in an aqueous solution of treating agent comprising 1,000 g. of ammonium sulfate. 500 g. of urea. 75 g. of

Temperature 01 heat treatment Tensile Tensile Adhesion stron th strength, por- Weight kg. 2 5 Weight kg./2.5 centago, loss, cm. of loss, cm. of Measurement percent 1 percent width percent idth Hlrmlulll llmrmmlng agent Nun! 83.3 0.86 88.4 3.10 Ammonium uultanmtc 50. 5S. 0 7. 24 71. 3 5. 2-1 Anminnium lml louulfonate 59. 2 53. 0 8. 00 69. 3 9. 0O Ammonium sulfite. 40.3 57.3 7. 53 72. 3 8. 53 Ammonium Lhlosullate 66. 6 52. 3 6.83 67. 8 7. 32 Ammonium sulfate-aniline (2:1 weight ratio) 41. 1 48. 7 7. 78 68. 3 8. 81 Ammonium blsultete-urea (1:1 molar ratio) 38.0 63. 0 7. 65 72. 1 8.70 Ammonium sulfite-triethanolamine (1 1.25

molar ratio).. 52.6 53. 3 7. 90 74. 9 8. 91 Ammonium thlosulfate-ur molar ratio). 37. 4 52.1 7.01 71. 3 8. 64 Ammonium sulfamete-urea (4:1 weight ratio). 40. 3 53. 8 7. 44 70. 1 9, 05 Ammonium imidosulfonate-thiourea (2:1

weight ratio) 50. 0 54. 2 8. 11 72. 6 9. 77 Sulfuric acid-urea (1 :2.75 molar ratio)- 39. 6 52. 5 8. 23 68. D 11. 56 Sulfuric aciu-thiourea. S1: 2 molar ratio) 34. 3 55. 3 4. 32 70. 2 6. 32 Sulfuric acid-triathano amine (1:3 molar ratio) 33. 4 57. 3 5. 74. 2 8. 42 Sulfuric acid guanidlne 24. 7 55. 3 6. 93 71.8 7. 98 Sullruie aoid.ethylenediamine 23. 1 59. 8 2. 80 75.0 3. 98 Sulfamic aoid-triethanolamine (1:1 molar 3 ratio) 38. 7 52. 3 5. 21 68. 8 7. 34 Sull'amic'acid-aniline (1:1 molar ratio) 53. 4 52. 3 3. 84 70. 5 5. 24 Sulfamic acid-ditzyandiamine. (1:1 molar ratio). 32. 4 53. 5 4. 12 75. 0 5. 12

tetrakis (hydroxymethyl)phosphoniuin chloride and 3,500 cc.

of water, wrung by a mangle and then dried so as to obtain treated cloth with the adhesion percentage .of solid Component being 50.4 percent. Subsequently, the thus treated cloth was charged in the same stainless steelcylinder as in example 3, after replacing the air in the cylinder by nitrogen, heated at a heating rate of 5? C./min. up to 500 C. and l,000 C. and heattreated at each temperature for 1 hour. The weight loss and tensile strength of the heat-treated cloth obtained are as follows:

The heat-treated cloth at 500 C. Weight loss: 48.5 percent; Tensile strength: 8.62 kg./2.5 cm. of width The heabtreated cloth at l,000 C.

Weight loss: 70.8 percent;

Tensile strength: 10.32 kg./2.5 cm. ofwidth.

EXAMlfLE s The same starting material diagonal cloth as in example 3 wassoaked in an aqueous solution of treating agent comprising 410 g. of sulfurous acid (net weight in sulfurous acid water), 750 g. of urea, g. of diammonium hydrogen phosphate and 2,000 cc. of water, wrung by mangle and then EXAMPLE 6 A bundle of viscose rayon fiber (denier of monofilament: 5.5 d; tensile strength: 1.9 g./d; elongation: 21.3 percent) is soaked in an aqueous solution of ammonium sulfate (400 g/l. lhereulter wrung and dried to obtain a bundle oftrcnted fibers with the adhesion percentage of ammonium sulfate being 59.3 percent. Subsequently, this bundle oftreuted fibers was heattreated in nitrogen by elevating the temperature at a rate of 1 C./min. over a range of from room temperature to 220 C., at a rate of 3 C./min. over a range of from 220 to 600 C. and at a rate of5 CJminfover a range of from 600 to 1,000 C. so as to obtain abundle of carbonlike fibers having a tensile strength of 3.3 g./d, elongation of 1.7 percent and carbon content of 90.3 percent. Subsequently, this bundle of carbonlike fibers was suspended perpendicularly in a graphite tube-shaped heatingbody (Tamnan furnace) having internal diameter of 2 cm. and heating portion length of 40 cm., a weight was suspended at the lower terminal of said bundle as a load of6.0 mg./d and the air in said heating body was replaced by argon. Thereafter, said treated bundle of fibers was heated in order to elevate the temperature from l,000 to 2,800C. in about 2 hours and further heattreated at 2,800 C. for l5 minutes. As the results, highly strong, flexible, heat resisting, excellent graphitelike fiber having a tensile strength of 3.5 g./d, elongation of 0.49 percent, Youngs modulus of l8,200 kgJmm. and carbon content of 99.9 percent was obtained.

A bundle of the same starting material fibers as in example 6 was soaked in an aqueous solution of treating agent comprising 490 g. of sulfuric acid, 600 g. of urea and 2,500 cc. of water, thereafter wrung and dried so as to obtain a bundle of treated fibers with the adhesion percentage of solid component being 57.0 percent. Subsequently, this bundle of fibers was heated in nitrogen up to l,000 C. and hcattreated in the same manner as in example 6 so as to obtain a bundle of carbonlike fibers with carbon content of 9 l .3 percent. Thereafter, this bundle of carbonlike fiber was suspended in the same graphite heating body as that of example 6, heated in argon from L000 to 2,800 C. in 2 hours and heattreated at 2,800 C. for 15 minutes. The obtained heat-treated fiber was graphitelike fiber having a tensile strength of 3.61 g./d, elongation of 0.45 percent, Young's modulus of 18,100 kgjmm. and carbon content of 99.9 percent.

What is claimed is:

1. A process for carbonizing cellulose fiber or the products thereof, which comprises the steps of:

a. treating cellulose fiber or the products thereof with a strength increasing agent selected from the group consisting of (A) ammonium sulfate, ammonium bisulfate, ammonium sulfite, ammonium bisulfite, ammonium thiosulfate, ammonium sulfnmatc. ammonium imidosulfonate, and mixtures thereof; (B) a mixture ofat least one compound selected from the group consisting of ammonium sulfate, ammonium blsulfate, ammonium sulfite, ammonium bisulfite, ammonium thiosulfate, ammonium sulfamate, and ammonium imidosulfonate with at least one organic nitrogen base, and (C) a mixture of an organic nitrogen base and an acid selected from the group consisting of sulfuric acid, sulfurous acid and sulfamic acid;

b. heattreating the product of step (a) in an inert atmosphere at a temperature of at least about 400 C. for a period of time sufficient to bring about carbonization.

2. The process of claim 1 in which the strength-increasing agent includes a flame resistance improving agent.

3. The process of claim 2 in which the flame-resistance-improving agent comprises at least one compound selected from 

2. The process of claim 1 in which the strength-increasing agent includes a flame resistance improving agent.
 3. The process of claim 2 in which the flame-resistance-improving agent comprises at least one compound selected from the group consisting of ammonium phosphate, guanidine phosphate, aluminum ammonium sulfate, and tetrakis (hydroxymethyl) phosphonium chloride.
 4. The process of claim 1 in which the strength-increasing agent is applied in the form of an aqueous solution.
 5. The process of claim 1 in which the heat treatment of step (b) is carried out at a heating rate of about 1* to about 5* C. per minute.
 6. The process of claim 1 in which the heat treating is effected at a temperature increasing up to not less than about 1,000* C. 